Tissue Engineering Projects

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3D Bioprinter for next generation of "bottom-up" tissue engineering

3D Bioprinter for next generation of "bottom-up" tissue engineering
Fraunhofer CMI worked under funding from Fraunhofer Gesellschaft on this project at the interface of engineering and life sciences to design and implement a novel hydrogel-based bioink embedded with mammalian cells, a 3D bioprinter, and automation software.

Viable endothelial cells in a Fraunhofer CMI bioprinted ring 24h post-printing. Live cells are shown in green while dead cells are shown in red.

Objective

The list of patients in dire need of organ transplants grows longer every day. Patients who are fortunate enough to find a 'match' still struggle with immunosuppressive therapy and ultimate organ failure. The goal of 3D bioprinting is to precisely place cells in environments that trigger their growth into fully functional tissues and organs. Fraunhofer CMI, and others involved in this effort, are working towards the ultimate goal of bioprinting the patient's own cells into a new and healthy replacement organ.

Methodology

Fraunhofer CMI's latest achievement in this field, was the development of a three-dimensional (3D) bioprinting system capable of multimaterial and multiscale deposition to enable the next generation of "bottom-up" tissue engineering. This area of research resides at the interface of engineering and life sciences, requiring an interdisciplinary team of engineers and scientists. Fraunhofer CMI's bioprinter has three components uniquely combined into a comprehensive tool: syringe pumps connected to a selector valve that allow precise application of up to five different materials with varying viscosities and chemistries, a high velocity/high-precision x–y–z stage to accommodate the most rapid speeds allowable by the printed materials, and temperature control of the bioink reservoirs, lines, and printing environment.

Results

Fraunhofer CMI’s custom-designed bioprinter is able to print multiple materials (or multiple cell types in the same material) concurrently with various feature sizes (100 μm–1 mm wide; 100 μm–1 cm high). One of these materials is a biocompatible, printable bioink that has been used to test for cell survival within the hydrogel following printing. Hand-printed (HP) controls show that our bioprinter does not adversely affect the viability of the printed cells.

Collaborators/Funding

This project is funded by Fraunhofer USA. New applications of the bioprinter to improve the osseointegration of hip implants is funded by Fraunhofer Gesellschaft and carried out by Fraunhofer CMI, Fraunhofer IGB and Fraunhofer IAP.

Future Directions

The researchers at Fraunhofer CMI are currently focused on improving osseointegration of hip implants and have successfully bioprinted scaffolds that support differentiation of bone cells.

Publication

Fraunhofer CMI reports the design and build of the 3D bioprinter, the optimization of the bioink, and the stability and viability of the printed constructs in their publication:

Frauhofer CMI has worked to develop a bioresponsive, biodegradable, microstructured material that can be grafted onto titanium implants to facilitate their osseointegration. Here, a support material (green) and gelatin hydrogel (GelMA) were bioprinted to form a 3D lattice structure.

Objective

A major clinical issue that limits the success of orthopedic implants is failure due to aseptic loosening driven by the incompatibility between the implant material (titanium) and osteoblasts (bone-forming cells). Creating a permanent, mechanically stable, biocompatible bond between the implant and the host bone is therefore crucial to the success of the implanted device. We sought to develop a bioresponsive, biodegradable, microstructured material that can be grafted onto titanium implants to facilitate their osseointegration.

Method

Realization of this project required (1) synthesizing custom hydrogels and optimizing its viscoelastic properties, (2) preparing titanium surfaces by chemical modification, (3) testing the interaction of osteoblasts with these hydrogels, and (4) designing and bioprinting lattices for osseointegration.

We worked primarily with a methacrylated gelatin (GelMA) coating that can be chemically grafted to the titanium surface. We impregnate the hydrogel with additional components to enhance the physical properties of hydrogels and osteogenesis. With this composite material, we printed microstructures with defined porosities with pores in the 150–400 μm size scale using our in-house developed bioprinter. To graft the engineered coating onto the titanium surface, we first activated the titanium surface to produce hydroxyl groups, and then silanized the surface.

Results

We optimized a protocol for the production of a hydrogel compatible with our bioprinting processes. Following UV curing, GelMA hydrogels were stable in tissue culture media or PBS at 37 °C for the duration of our experiments (up to 2 months) under these conditions. We were also able to graft GelMA hydrogels to a titanium surface by solution-based chemistry.

We designed a modified log cabin structure that incorporated a gelatin support material that would simply dissolve at 37 °C leaving the UV-cured GelMA lattice intact. We printed this GelMA lattice with three layers at 250 μm each. We found that bone cells growing on GelMA lattices thrive and form large connective structures that deposit new calcium mineral, suggesting mature differentiation and formation of bone-like material. These bone cells growing under the same conditions on smooth GelMA films did not appear to deposit calcium mineral, indicating the importance of bioprinted lattices for osseointegration.

Future Directions

With our collaborators, we are continuing to develop new materials and printing methods to achieve the goals of biomimetic osseointegration.